A jury has convicted five New Orleans police officers of shooting dead two African Americans during the chaos unleashed by Hurricane Katrina in 2005 and trying to cover-up the killings.

The police officers were found guilty on 25 counts and could now face life imprisonment after being convicted of the deaths of two unarmed African American civilians in the days after Katrina devastated the southern town.

"This shows that law enforcement officers will be held accountable for their actions," US attorney Jim Letten said after the guilty verdict was handed down.

"The culture that fostered this code of silence is being shattered every day."

The trial focused on events on the morning of September 4, 2005, on the city's Danziger Bridge when officers, responding to a call of shooting in the area, let off what prosecutors have described as a "hail of gunfire".

Ronald Madison, a 40-year-old mentally disabled man described by family members as gentle and loving, was shot several times in the back and died at the scene.

One of the officers, Kenneth Bowen, also stamped on him while he lay wounded.

James Brisette, 17, a high school student who friends said was nerdy and studious, also died on the bridge.

Four others people from the same family were also wounded.

"The officers convicted today abused their power and violated the public's trust during the aftermath of Hurricane Katrina - exacerbating one of the most devastating times for the people of New Orleans," attorney-general Eric Holder said in a statement.

Katrina smashed through the city's poorly maintained levees on August 29, 2005, causing the Gulf to flood in swallowing up 80 per cent of New Orleans and leaving thousands stranded on their rooftops.

Reports of widespread looting and armed gangs roaming the city shifted the government's already botched response to the disaster from humanitarian aid to a military operation.

'Post-apocalyptic justice'

Prosecutors and family members of the victims said the verdict brings some closure to a six-year struggle for justice, but in many ways the trial was a referendum on two differing views of the days after Katrina.

Defence lawyers had said the five officers were heroes who rescued people and "fought bad guys" in a chaotic and lawless city.

They had sought to convince the jury that the officers believed their lives were in danger.

But in her closing arguments, Bobbi Bernstein, deputy chief of the US Justice Department's civil rights division, rejected the idea that the officers were heroes, saying the grieving relatives deserved more.

She claimed an official cover-up had "perverted" the system, adding "the real heroes are the victims who stayed with an imperfect justice system that initially betrayed them".

Officers "delivered their own kind of post-apocalyptic justice," she added.

"The law is what it is because this is not a police state."

As the judge read out the verdicts, tears streamed down the faces of some of the relatives, while the mother of one of the officers buried her face in her hands.

Speaking after the verdict, Sherrel Johnson, the mother of Mr Brisette, said the officers, "took the twinkle out of my eye, the song out of my voice, and blew out my candle," when they killed her son.

The sister of Mr Madison, Jacqueline Madison Brown, told reporters: "Ronald Madison brought great love to our family. Shooting him down was like shooting an innocent child."

The family regretted that some officers, who had testified for the prosecution in exchange for lesser charges, "did not have the courage and strength to come forward sooner," she said.

Kenneth Bowen, Robert Gisevius, Anthony Villavaso, and Robert Faulcon, the officers involved in the shooting, could now receive life sentences.

Their supervisor Sergeant Arthur Kaufman, who was not on the bridge, but was convicted of leading the conspiracy, could receive a maximum of 120 years.

Kaufman joined the other four defendants in trying to cover-up what had happened. He got a gun from his home and claimed to have found it on the bridge.

He also made up false witnesses and coached the other officers on getting their stories straight before they made their formal statements.

You have no doubt been hearing a lot about the Paris Agreement and know that it pertains to climate change, but are too embarrassed at this stage to ask for an overall explanation of what it's all about.